1. Field of Invention
The invention relates to a machine and a method for printing material webs as described herein.
2. Description of the Prior Art
Printed materials are examined in order to check the printing results. Generally, for this purpose a finished printed product is removed and examined for its optical impression, among other things. Recently, printed material webs are increasingly observed inline via sensors, such as cameras, in order to continuously monitor the result of the printing process and to come to a conclusion faster. DE 10 2004 007 374 B3 also shows a device for the inline web monitoring. In this publication the web to be examined is guided by a counter support in the area of the web observation station. Here, the counter support is positioned on the side of the web facing away from the sensor. The counter support shows a porous or perforated surface through which air is pressed. As a consequence of this measure an air pocket forms, on which the web glides.
Experience has shown that measuring errors occur in the inline web observation stations shown above. This particularly applies when color impressions of transparent or partially transparent printed materials are examined. Additionally, some opaque materials may be problematic, here.